Plot: It was a blatant rip-off of The Terminator, with an add in from the film The Fury.
Guy comes from the future to change the past by eliminating the child who will mess up the future.
There are three targets.
He was even so blatant as to name the heroin Sarah. Seriously?
Seeking a child with dangerous psychic powers to eliminate him (while we know this from the start in The Fury, here we find out later).
Gordon-Levitt sacrifices himself at the end to save the heroin and her child just as Reece does in Terminator (Reece's sacrifice isn't as effective, obviously).
Characters: Joseph Gordon-Levitt was Reece, Bruce Willis was the Terminator, Emily Blunt was Sarah Connor, the kid was a combination of John Connor and Andrew Stevens' character from The Fury.
Scenes: Willis' character goes into the bad guys' HQ and guns down everyone = Terminator smashes into the police station and guns down everyone.
Kid loses it and uses his mental powers to blow up Jesse and the living room = Amy Irving uses her mental powers to blow up John Cassavetes at the climax to The Fury.
Willis getting supplies, then threatening to shoot the clerk = Terminator getting rifles and ammo, then shooting the clerk.
Sarah decides she loves Gordon-Levitt and has sex with him = Sarah decides she loves Reece and has sex with him (which was actually a key to the plot while here it was rather pointless)
Can't quite recall, but the shootout at the diner and Willis escaping by jumping through the window is from another film, too.
There was at least one other scene stolen directly from Terminator, but now I can't recall what it was.